1. Field of the Invention
The present invention relates to a holding head for holding an object such as an electric component (e.g., an electronic component) and particularly to such a holding head which includes a suction nozzle for applying a negative pressure to a back surface of an object and thereby holding the object and a back-surface lighting device for lighting the back surface of the object held by the suction nozzle.
2. Related Art Statement
The above-indicated holding head is employed by, e.g., an electric-component mounting device which mounts an electric component on a printed circuit board (xe2x80x9cPCBxe2x80x9d). In the electric-component mounting device, the holding head receives an electric component from an electric-component supplying device and mounts the component at a predetermined position on the PCB. Even if the current X-direction and Y-direction positions of the component held by the holding head are deviated from respective reference positions, the component can be accurately mounted at the predetermined position on the PCB, by moving the holding head to a corrected or modified position deviated from the predetermined position by respective distances between the X-direction and Y-direction positions of the component and the corresponding reference positions. To this end, it is needed to measure the respective distances between the X-direction and Y-direction positions of the component held by the holding head and the corresponding reference positions, and to measure them, it is widely practiced that an image taking device takes a silhouette image of the component. To take a silhouette image of the component held by the holding head, it is needed to light the back surface of the component that is held by the holding head. To this end, it has widely been practiced that the suction nozzle and a main portion of the back-surface lighting device are constructed as an integral unit. For example, a light emitting plate including a plurality of point light sources, such as light emitting diodes, and a diffusing layer for diffusing the lights emitted by the point light sources and thereby emitting a substantially uniform light, is fixed to the suction nozzle, or alternatively a light emitting plate which absorbs infrared rays externally incident thereto and emits a visible light, a reflecting plate which reflects a light externally incident thereto, or a diffusing block which diffuses a light externally incident thereto and emits a light toward the suction nozzle, is fixed to the suction nozzle.
However, if the main portion of the back-surface lighting device is provided as the integral portion of the suction nozzle, the suction nozzle costs high. Generally, the suction nozzle includes a suction pipe, which may be bent to be not usable or whose suction surface (i.e., free end surface) may be worn to be not usable. If the main portion of the back-surface lighting device is provided as the integral portion of the suction nozzle, the suction nozzle as a whole including the main portion of the back-surface lighting device must be replaced with another suction nozzle including a main portion of another back-surface lighting device. This manner leads to increasing the running cost of the electric-component mounting device. Meanwhile, in the case where a plurality of sorts of suction nozzles are exchanged with one another corresponding to a plurality of sorts of electric components to be held, the number of suction nozzles employed increases. If each of those suction nozzles includes a main portion of a back-surface lighting device, the running cost costs very high. Moreover, in the case where the main portion of each back-surface lighting device includes a light emitting source, the light emitting source must be supplied with electric power. In the last case, when the suction nozzles are repetitively exchanged with one another, the contact of an electric-power supply circuit which supplies the electric power to the light emitting source may be worn or damaged, or an electric noise may be produced from the contact.
While the foregoing explanation relates to the holding head which is for holding electric components, objects to be held by the holding head are not limited to the electric components. The above-explained problems may commonly occur to all objects that can be held by suction nozzles and whose images need to be taken to recognize each object by image processing or to determine X-direction, Y-direction, and rotation positions of each object, measure one or more dimensions of each object, etc.
The present invention provides a holding head and a transferring apparatus that has one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (9). Any technical feature which includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that technical feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the combinations thereof are just examples to which the present invention is by no means limited.
(1) According to a first feature of the present invention, there is provided a holding head comprising a support portion; a suction nozzle which applies a negative pressure to a back surface of an object and thereby holds the object, the suction nozzle being detachably attached to the support portion; and a back-surface lighting device which lights the back surface of the object held by the suction nozzle and which includes a main portion which is separate from the suction nozzle and is supported by the support portion such that when the suction nozzle is detached from the support portion, the main portion remains supported by the support portion. In the present holding head, the suction nozzle can be detached from the support portion, while the main portion of the back-surface lighting device remains supported by the support portion. For example, in the case where the free end surface of a suction pipe of the suction nozzle is so worn as to be not usable or the suction pipe is so bent as to be not usable, the suction nozzle including the suction pipe can be removed from the support portion and be replaced with a new suction nozzle, while the main portion of the back-surface lighting device still remains on the support portion for further use with the new suction nozzle. This feature contributes to decreasing the running cost of the holding head. In the case where a plurality of sorts of suction nozzles are exchanged with one another corresponding to a plurality of sorts of objects to be held, the main portion of the single back-surface lighting device may be commonly used with each selected one of the different sorts of suction nozzles. This feature also contributes to decreasing the running cost of the holding head. Moreover, even in the case where the main portion of the back-surface lighting device includes a light emitting source, the main portion need not be detached from the support portion when the different sorts of suction nozzles are exchanged with one another. This feature solves the problems that the contact of an electric-power supply circuit is worn or damaged and an electric noise is produced from the contact. According to the present invention, a portion of the back-surface lighting device may be provided as an integral portion of the suction nozzle or each of the different sorts of suction nozzles. In this case, the suction nozzle, or each suction nozzle, including the portion of back-surface lighting device is attached to, and detached from, the support portion of the holding head. Alternatively, the entirety of the back-surface lighting device may be directly supported by the support portion of the holding head. In the last case, when the suction nozzle is detached from the support portion, no portion of the back-surface lighting device is detached from the support portion.
(2) According to a second feature of the present invention that includes the first feature (1), the main portion of the back-surface lighting device comprises a tubular lighting portion which emits, from an inner surface thereof, a first light; and an outer lighting portion which extends outward from the tubular lighting portion and which emits, from one surface thereof, a second light in a direction parallel to a centerline of the tubular lighting portion, and wherein the suction nozzle comprises a light converting portion which is fitable in an inner space of the tubular lighting portion and which converts the first light emitted by the tubular lighting portion into a third light having the direction parallel to the centerline of the tubular lighting portion; and a suction pipe which holds the object and which extends from one end of the light converting portion in the direction parallel to the centerline of the tubular lighting portion, one end portion of the suction nozzle that is opposite to the suction pipe being detachably attached to the support portion. In the present holding head, the suction nozzle includes, in addition to the suction pipe, the light converting portion as a portion of the back-surface lighting device. In the state in which the suction nozzle is attached to the support portion of the holding head, the light converting portion is positioned in the inner space of the tubular lighting portion, and converts the light emitted from the inner surface of the tubular lighting portion into a light having a direction parallel to the centerline of the tubular lighting portion. Thus, the back surface of the object held by the suction pipe is lighted with a sufficient amount of light even in the vicinity of the pipe, and a clear silhouette image of the object can be taken by an image taking device. It is preferred that the inner surface of the tubular lighting portion has a circular cross section. However, the inner surface may have a square cross section or any other appropriate shape. The second feature (2) may not be combined with the first feature (1) wherein the suction nozzle can be detached from the support portion while the main portion of the back-surface lighting device still remains supported by the support portion. That is, a holding head may employ the second feature (2), independent of the first feature (1).
(3) According to a third feature of the present invention that includes the second feature (2), at least one of the tubular lighting portion and the outer lighting portion comprises a plurality of point light sources which emit respective lights and which are arranged on a plurality of lattice points, respectively; and a diffusing layer which diffuses the lights emitted by the point light sources and thereby emits a substantially uniform light. In the present holding head, the back-surface lighting device includes the point light sources and accordingly can emit lights to light the back surface of the object held by the suction nozzle. The point light sources may be provided by point light-emitting elements such as light emitting diodes, or by respective end surfaces of optical fibers each of which transmits a light emitted by, e.g., a halogen lamp, the end surfaces being arranged on lattice points, respectively. In the case where the point light sources are provided by the point light-emitting elements, the point light-emitting elements need the supply of electric power. However, the point light-emitting elements can remain on the support portion when the suction nozzle is detached from the support portion. Therefore, an electric-power supply circuit which supplies the electric power to the point light-emitting elements need not be provided with a contact that is frequently connected and disconnected. Thus, the present holding head is free of the problems that the contact is damaged and an electric noise is produced from the contact. In the case where the point light sources are provided by the end surfaces of optical fibers, the optical fibers need to be connected to the tubular and/or outer lighting portions. However, when the suction nozzle is detached from the support portion, the tubular and outer lighting portions remain on the support portion. Thus, the present holding head does not need any means for facilitating the connection and disconnection of the optical fibers, and accordingly can enjoy a simpler construction.
(4) According to a fourth feature of the present invention that includes the second or third feature (2) or (3), the light converting portion comprises a tapered reflecting surface which is coaxial with the suction pipe and whose radius increases in a direction away from a free end of the suction pipe that holds the object. The tapered reflecting surface can easily deflect the light emitted radially inward from a cylindrical inner circumferential surface of the tubular lighting portion, to a direction substantially parallel to an axis line of the suction pipe.
(5) According to a fifth feature of the present invention that includes the second or third feature (2) or (3), the light converting portion comprises a diffusing block which diffuses the first light emitted by the tubular lighting portion and emits the third light from an outer surface thereof located on a side of the suction pipe. The diffusing block receives, at the outer surface thereof, the light emitted from the inner surface of the tubular lighting portion, and diffuses therein the received light so that the block becomes lighter as a whole. Accordingly, a light is emitted toward the object held by the suction pipe from a pipe-side surface of the diffusing block.
(6) According to a sixth feature of the present invention that includes any one of the second to fifth features (2) to (5), the holding head further comprises a support rod which is supported by the support portion such that the support rod is movable in a direction parallel to an axis line of the suction pipe; an attaching device which attaches the suction nozzle to one end portion of the support rod such that the suction nozzle is detachable from the support rod; and a support-rod moving device which moves the support rod in a direction parallel to an axis line thereof, thereby moving the light converting portion of the suction nozzle relative to the tubular lighting portion in the direction parallel to the centerline thereof, so that the suction pipe of the suction nozzle is advanceable and retractable in the direction parallel to the axis line thereof. In the present holding head, the suction nozzle including the light converting portion and the suction pipe is attached to the support portion via the support rod, and the support rod is moved, by the support-rod moving device, relative to the support portion in an axial direction of the rod, so that the suction pipe is advanced and retracted in an axial direction thereof. The advancing and retracting movements of the suction pipe can be utilized for, e.g., causing the pipe to hold the object or mount the object on a mount surface. For example, in the case where the object is an electric component, the suction pipe can be caused to take the component from an electric-component supplying device and mount the same on a PCB. In this case, since the main portion of the back-surface lighting device need not be advanced or retracted with the suction nozzle, the nozzle can be quickly advanced and retracted while being prevented from producing vibration or noise. Thus, the present holding head can mount electric components with high efficiency. In addition, the main portion of the back-surface lighting device can be effectively prevented from interfering with electric components which have already been mounted on the PCB, and the force with which the suction nozzle contacts each electric component and/or the force with which the nozzle presses each component on the PCB can be accurately controlled.
(7) According to a seventh feature of the present invention that includes any one of the second to sixth features (2) to (6), the main portion of the back-surface lighting device further comprises an auxiliary lighting portion which is opposed to a gap provided between the tubular lighting portion and the light converting portion and which emits a fourth light toward a side of the suction pipe via the gap. In the present holding head, the auxiliary lighting portion lights the gap provided between the tubular lighting portion and the outer lighting portion. Accordingly, the back surface of the object is lighted with a uniform light and a clear silhouette image of the object can be obtained.
(8) According to an eighth feature of the present invention, there is provided a transferring apparatus comprising a holding head according to any one of the first to seventh features (1) to (7); a moving device which moves the holding head in a direction perpendicular to the axis line of the suction pipe; and an image taking device which is provided at a predetermined position in a range in which the moving device moves the holding head, so that when the holding head is positioned at the predetermined position, the image taking device is opposed to the holding head and takes an image of the object held by the holding head. The range in which the holding head is moved may be a one-dimensional, two-dimensional, or three-dimensional range. In the present transferring apparatus, the object is held by the holding head, which in turn is moved by the moving device, so that the holding head is opposed to the image taking device. Thus, a silhouette image of the object held by the holding head can be taken by the image taking device. Image data representing the thus taken silhouette image may be processed to identify the object, determine one or more positions of the object held by the holding head, and/or measure one or more dimensions of the object. For example, in the case where the object is an electric component, the holding head receives the electric component from an electric-component supplying device, transfers it, and mounts it on a PCB. Before the holding head mounts the component on the PCB, the image taking device takes an image of the component held by the suction nozzle, and the taken image is processed to determine one or more sorts of positional errors of the component held by the nozzle. After the positional errors of the component are corrected, the holding head mounts the component on the PCB.
(9) According to a ninth feature of the present invention that includes the eighth feature (8), the transferring apparatus further comprises a nozzle stocker which stocks at least one suction nozzle; and a nozzle-exchange control device which controls the moving device to move the holding head to a position where the holding head is opposed to the nozzle stocker, and causes the suction nozzle attached to the holding head to be exchanged with the one suction nozzle stocked by the nozzle stocker. In the present transferring apparatus, the moving device for transferring the object held by the holding head is additionally used for automatically exchanging the suction nozzles with each other. Thus, the transferring apparatus capable of automatically exchanging the suction nozzles can be produced at low cost.